.mask {
  margin: 0;
  padding: 0;
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  font-family: "montserrat";
  background-image: linear-gradient(125deg, #2c3e50, #27ae60, #2980b9, #e74c3c, #8e44ad);
  background-size: 400%;
  animation: bganimation 15s infinite;
  z-index: 99;

}


@keyframes bganimation {
  0% {
    background-position: 0% 50%;
  }

  50% {
    background-position: 100% 50%;
  }

  100% {
    background-position: 0% 50%;
  }
}